CDKN1A and neoplasm: Indeed, such p53/pRb-independent p21CIP1 activation in non-tumor alveolar parenchyma may reflect a rapid BRAFV600E-mediated cytotoxic response reminiscent to that observed in CCs (see below), thus suggesting that albeit BRAFV600E ATIIs are prone to give rise to adenomas, yet there is an immediate cell cycle arrest in a minority of the challenged ATIIs.